"Oddsmakers move lines in response to where the public places bets in order to keep an even distribution of money across all markets." http://www.betsmart.co/how-do-oddsmakers-set-lines/ [emphasis added]
Ask yourself the above question in a different way---"Do I really believe that it's plausible for Joe Biden to win big, yet lose House seats and under-perform in The Senate (ie no coattails)?"
Yes.A lot of moderate and never Trumper republicans as well as independents wanted Trump out but wants a GOP Congress to prevent Democrats from going to far left. If you hate Trump but don't want court packing,ending the filibuster,adding new states etc than you vote Biden for President and republicans for Congress.
The answer to this question is of course, no it's not plausible. ----10 or 11 million more folks voted for Trump this time around than last time, so any argument made that folks, especially Republicans, were out to vote against him is a failed position. In fact, if you answered yes to the above question, then you are admitting that The Trump agenda won and that no one wants the Biden/Harris agenda. What that would mean is that should Biden be elected, he would be a lame duck president right from the start.
Cindy McCain,John Kasich,Rick Synder,Lincoln protect founders and millions of other republicans would disagree.
Amazing that so many don't know how this works. How Do Oddsmakers Set Lines? http://www.betsmart.co/how-do-oddsmakers-set-lines/ "Oddsmakers move lines in response to where the public places bets in order to keep an even distribution of money across all markets. See our page on Sportsbook Margins for an explanation of why books want even distribution across markets. ..."